In very simple words, I will say that light is an electromagnetic radiation of wide range and the part of it which can be detected by the human eye is called the visible light. The visible light is the basic medium to see each other and perceive things around us.
Light is a source of life on earth. It keeps our earth warm, helps plants in synthesizing their food which in return provide us fresh oxygen to inhale.
The electromagnetic radiations occur over a wide spectrum from gamma rays having wavelength as low as (100 picometers, one-trillionth of a meter) to radio waves in meters.
But our human eyes can detect wavelengths of very narrow range from 700 nanometers (red) to 400 nanometers (violet) and this is called the visible band of the electromagnetic spectrum.
(1 nanometer = 1 billionth of a meter)
In other words, we can say that the visible light is the small subset of the wide electromagnetic spectrum.
The spectral band adjacent and above the violet region is called as Ultra-violet region and the band below the red region of the visible band is called as the infrared region of the electromagnetic spectrum.
The electromagnetic spectrum is shown below:
What are electromagnetic radiations?
The electromagnetic radiations are a form of energy which is present all around us. And sunlight is a form of electromagnetic radiations.
The electromagnetic waves are produced when a charged particle says an electron is accelerated under the influence of the electric field. This results in the production of the electric field and the magnetic mutually perpendicular to each other and also to the wave propagation.
E = Electric field
B = Magnetic field
C = Direction of wave propagation
You can see that all the three are perpendicular to each other
Dual nature of light
The light has dual nature one is wave nature (due to interference effect in light beams, implying that light is made up of waves) and the other is particle nature (the photoelectric effect supports the particle nature of light and the light may be viewed as packets of energy called photons).
However, to know the complete nature of light at any moment requires a detailed analysis which is seldom required while studying the photo-voltaic solar power system.
Therefore, I am limiting my discussion about the dual nature of light as an introduction and is enough at this point.
Characteristics of light important for solar photo-voltaics
However, there are certain characteristics of light which are required while studying and designing the solar power system and these are as follows:
The energy corresponds to 1127 nm wavelength is sufficient enough to send electrons from the valence band to the conduction band by jumping the band gap. The less energy may not be able to pluck the electrons while more energy than required results in heating and reduces the performance of the panel.
It is because of the reason that specific wavelength is necessary for the solar panels to perform, the efficiency of the solar cells is limited. The maximum efficiency of the single layer silicon cell until now is around 24%.
However, recent developments in the quantum dot technology have made it possible to increase the efficiency of the solar panels beyond their theoretical limit of 33.3%